This invention relates to a data transmission device for transmitting data via a transmission line, and more particularly, to a data transmission device which can change the number of lanes of a transmission line.
Recently, in the field of data transmission over a long distance, an increase in transmission speed has been saturated for a method of data transmission in a single channel (also referred to as lane). To address this problem, in order to increase the communication bandwidth, a technology of combining a plurality of lanes so as to be considered as a single link has been developed (lane bonding and deskewing between multi-lanes).
IEEE Std. 802.3-2005, Clause 48, “Physical Coding Sublayer (PCS) and Physical Medium Attachment (PMA) sublayer, type 10 GBASE-X” describes a method of transmission over a plurality of lanes as a standardized technology for 10 Gb/s Ethernet. The 10 Gb/s Ethernet combines four lanes of 2.5-Gbps data to realize a transmission speed of 10 Gbps. For the transmission method employing a plurality of lanes, there is a problem of correcting differences in arrival time of data caused by differences in transmission distance among lanes and, for optical transmission, differences in light wavelength in the respective lanes (referred to as skew).
For the 10 Gb/s Ethernet, a transmitter transmits an align column (∥A∥), which is a special control code of an 8B/10B code, simultaneously on the combined four lanes, and a receiver calculates differences in arrival time of the align column for the respective lanes.
IEEE Std. 802.3-2005, Clause 48, “Physical Coding Sublayer (PCS) and Physical Medium Attachment (PMA) sublayer, type 10 GBASE-X” does not detail a method of correcting the skews based on the calculated differences in arrival time of the align column. However, generally, the skew is corrected by buffering arriving data using a FIFO buffer or a variable-delay circuit by a quantity of the skew specific to the respective lanes.
According to Japanese Patent Application Laid-open No. 2004-193817, a transmitter periodically transmits a patterned signal (data pattern for deskewing), and a receiver generates, based on the received data pattern for deskewing, a clock having a long period, thereby calculating a phase difference of clocks of the respective lanes (namely, skews). The method for correcting the calculated skews is the same as the above-mentioned method employing a FIFO buffer or a variable-delay circuit.